Messages in this thread Patch in this message | | | Date | Fri, 5 Sep 2008 09:30:14 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [BUG] x86 kenel won't boot under Virtual PC |
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On Fri, 5 Sep 2008, David Sanders wrote: > > The patch disables a optimization used in one place by commenting out some > lines in nop.h. Please comment.
Hmm.. I'm not a huge fan of the ASM_NOP mess, but you also disable it for 64-bit x86 too.
On 32-bit, at least the generic nops are fairly reasonable, but the default nops for 64-bit really look pretty sad, and the P6 nops really do look better.
So I would suggest perhaps moving the static P6 nop selection into the CONFIG_X86_64 thing.
The alternative is to just get rid of that static nop selection, and just have two cases: 32-bit and 64-bit, and just pick obviously safe cases for them.
So I think that particular part would be better off with changing the Kconfig language instead. Ie something like this..
(I removed the 32-bit CPU's from the choices, except for MPENTIUM4 that really should be merged with MPSC - the difference between MPENTIUM4 and MPSC seems to be just a totally bogus 32-bit vs 64-bit thing. Yes, yes, there are PENTIUM4's without 64-bit, but there are also Prescott chips that run 32-bit kernels, so the thing is a bit confused.
Linus
--- arch/x86/Kconfig.cpu | 13 ++++++++----- 1 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index 2c518fb..b225219 100644 --- a/arch/x86/Kconfig.cpu +++ b/arch/x86/Kconfig.cpu @@ -382,14 +382,17 @@ config X86_OOSTORE # P6_NOPs are a relatively minor optimization that require a family >= # 6 processor, except that it is broken on certain VIA chips. # Furthermore, AMD chips prefer a totally different sequence of NOPs -# (which work on all CPUs). As a result, disallow these if we're -# compiling X86_GENERIC but not X86_64 (these NOPs do work on all -# x86-64 capable chips); the list of processors in the right-hand clause -# are the cores that benefit from this optimization. +# (which work on all CPUs). In addition, it looks like Virtual PC +# does not understand them. +# +# As a result, disallow these if we're not compiling for X86_64 (these +# NOPs do work on all x86-64 capable chips); the list of processors in +# the right-hand clause are the cores that benefit from this optimization. # config X86_P6_NOP def_bool y - depends on (X86_64 || !X86_GENERIC) && (M686 || MPENTIUMII || MPENTIUMIII || MPENTIUMM || MCORE2 || MPENTIUM4 || MPSC) + depends on X86_64 + depends on (MCORE2 || MPENTIUM4 || MPSC) config X86_TSC def_bool y
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